The present invention relates to a gas circuit breaker of grounded-tank type, particularly, a gas circuit breaker of grounded-tank type which has an interrupting device, a resistor device and a capacitor device, and in which the interrupting device, the resistor device and the capacitor device are connected in parallel
A conventional gas circuit breaker for high voltage and large current has interrupting devices 1 and impedance devices each of which is connected with the interrupting device in parallel as shown in FIG. 18. The conventional impedance device has a capacitor device for decreasing a transient recovery voltage of the interrupting device 1 and for dividing appropriately the voltage of the gas circuit breaker among the interrupting devices 1, and a resistor device 19 which has a resistor element 23 and a resistor contact 19A to decrease a surge during connecting.
A main interrupting device and so forth are contained in a cylindrical container (grounded tank) which is filled with insulating gas such as SF6 gas having high dielectric strength and arc-extinguishing efficiency. Since the high dielectric strength and arc-extinguishing efficiency of this kind of gas is obtained in uniform electric field strength, the interrupting device is covered by a shield cylinder and the shield cylinder faces on an inner surface of the grounded tank so that an insulation between the interrupting device and the grounded tank is maintained. Therefore, the structure arranged in the shield cylinder is important for decrease of a diameter of the grounded tank. The conventional gas circuit breaker has the interrupting device 1 which includes a fixed contact and a movable contact moving away from or to the fixed contact in a direction parallel to the axis of the grounded tank to interrupt or flow the current, the capacitor device 2 and the resistor device 19 which includes the resistor element 23 and the resistor contact 19A, all of the interrupting device, the capacitor device and the resistor device are contained compactly in a cylindrical shield having a large diameter at the area of the interrupting device and the arrangement of the devices are designed appropriately so that the whole of the interrupting device is effectively inspected. (Refer to Japanese Examined Patent Publication No. 57-21819 and Japanese Unexamined Patent Publication No. 60-25123.) In such circuit breakers, an opening for inspecting the interrupting device is arranged at a surface of the tank facing on the main interrupting device 1 and the capacitor device 2, the resistor element and elements relating thereto are not arranged between the interrupting device 1 and the opening for inspection. In new gas circuit breaker, the voltage interrupted by the main interrupting device increases and the number of the elements constituting the interrupting device for interrupting one phase decreases, for example, the number of the interrupting device per phase in the circuit breaker for 550 kV is one.
There are following problems for constructing the circuit breaker with one interrupting device per phase and for increasing dielectric strength for high voltage. For instance, in order to construct the circuit breaker with one interrupting device per phase, the capacitor device having the dielectric strength corresponding to the dielectric strength of the conventional circuit breaker including two interrupting devices per phase must be arranged in the circuit breaker including one interrupting device per phase. Since the transient recovery voltage is interrupted by one interrupting device, quadruple space for containing the capacitor device is necessary in comparison with the circuit breaker including two interrupting device so that the rising rate of the transient recovery voltage is sufficiently decreased. Further, in order to increase the dielectric strength, the local electric field strength must be decreased. But since the distance between the fixed side cylindrical shield covering the main fixed contact and the fixed resistor contact and the movable side cylindrical shield covering the main movable contact and the movable resistor contact is substantially equal to the distance between the contacts of the interrupting device, there is a problem that the length of the capacitor device is more than three times as long as the distance between the cylindrical shields. As above mentioned, in the circuit breaker having close distance between the cylindrical shields. Since isoelectric liens are extended or arranged by the capacitor device, there is a problem that the local electric field strengths increase between the point of the shield of the fixed main contact and the point of the movable main contact and between the ends of the cylindrical shields facing to each other. If a distance between the interrupting device and the capacitor device and/or a distance between the capacitor device and the shields are increased in order to decrease the deflection of the isoelectric liens extended by the capacitor device, the outer diameters of the cylindrical shields are increased, so that the size of the circuit breaker is increased.